序

• Go 设计模式实现，包含常见的设计模式实现，同时这也是 极客时间-设计模式之美 的笔记，源课程采用 Java 实现，本系列会采用 Go 实现
• 课程: 56 | 观察者模式（上）：详解各种应用场景下观察者模式的不同实现方式
• 本文代码仓库: https://github.com/mohuishou/go-design-pattern 🌟🌟🌟🌟🌟
• RoadMap: 13/22 持续更新中，预计一周更新 2 ~ 3 种设计模式，预计到 202010 月底前更新完成
• 获取更新: Github、知乎、RSS、开发者头条 **

笔记

代码实现

基础实现

Code

package observer

import "fmt"

// ISubject subject
type ISubject interface {
	Register(observer IObserver)
	Remove(observer IObserver)
	Notify(msg string)
}

// IObserver 观察者
type IObserver interface {
	Update(msg string)
}

// Subject Subject
type Subject struct {
	observers []IObserver
}

// Register 注册
func (sub *Subject) Register(observer IObserver) {
	sub.observers = append(sub.observers, observer)
}

// Remove 移除观察者
func (sub *Subject) Remove(observer IObserver) {
	for i, ob := range sub.observers {
		if ob == observer {
			sub.observers = append(sub.observers[:i], sub.observers[i+1:]...)
		}
	}
}

// Notify 通知
func (sub *Subject) Notify(msg string) {
	for _, o := range sub.observers {
		o.Update(msg)
	}
}

// Observer1 Observer1
type Observer1 struct{}

// Update 实现观察者接口
func (Observer1) Update(msg string) {
	fmt.Printf("Observer1: %s", msg)
}

// Observer2 Observer2
type Observer2 struct{}

// Update 实现观察者接口
func (Observer2) Update(msg string) {
	fmt.Printf("Observer2: %s", msg)
}

单元测试

package observer

import "testing"

func TestSubject_Notify(t *testing.T) {
	sub := &Subject{}
	sub.Register(&Observer1{})
	sub.Register(&Observer2{})
	sub.Notify("hi")
}

使用 Golang 实现 EventBus

我们实现一个支持以下功能的事件总线

1. 异步不阻塞
2. 支持任意参数值

Code

package eventbus

import (
	"fmt"
	"reflect"
	"sync"
)

// Bus Bus
type Bus interface {
	Subscribe(topic string, handler interface{}) error
	Publish(topic string, args ...interface{})
}

// AsyncEventBus 异步事件总线
type AsyncEventBus struct {
	handlers map[string][]reflect.Value
	lock     sync.Mutex
}

// NewAsyncEventBus new
func NewAsyncEventBus() *AsyncEventBus {
	return &AsyncEventBus{
		handlers: map[string][]reflect.Value{},
		lock:     sync.Mutex{},
	}
}

// Subscribe 订阅
func (bus *AsyncEventBus) Subscribe(topic string, f interface{}) error {
	bus.lock.Lock()
	defer bus.lock.Unlock()

	v := reflect.ValueOf(f)
	if v.Type().Kind() != reflect.Func {
		return fmt.Errorf("handler is not a function")
	}

	handler, ok := bus.handlers[topic]
	if !ok {
		handler = []reflect.Value{}
	}
	handler = append(handler, v)
	bus.handlers[topic] = handler

	return nil
}

// Publish 发布
// 这里异步执行，并且不会等待返回结果
func (bus *AsyncEventBus) Publish(topic string, args ...interface{}) {
	handlers, ok := bus.handlers[topic]
	if !ok {
		fmt.Println("not found handlers in topic:", topic)
		return
	}

	params := make([]reflect.Value, len(args))
	for i, arg := range args {
		params[i] = reflect.ValueOf(arg)
	}

	for i := range handlers {
		go handlers[i].Call(params)
	}
}

单元测试

package eventbus

import (
	"fmt"
	"testing"
	"time"
)

func sub1(msg1, msg2 string) {
	time.Sleep(1 * time.Microsecond)
	fmt.Printf("sub1, %s %s\n", msg1, msg2)
}

func sub2(msg1, msg2 string) {
	fmt.Printf("sub2, %s %s\n", msg1, msg2)
}
func TestAsyncEventBus_Publish(t *testing.T) {
	bus := NewAsyncEventBus()
	bus.Subscribe("topic:1", sub1)
	bus.Subscribe("topic:1", sub2)
	bus.Publish("topic:1", "test1", "test2")
	bus.Publish("topic:1", "testA", "testB")
	time.Sleep(1 * time.Second)
}

结果

=== RUN   TestAsyncEventBus_Publish
sub2, testA testB
sub2, test1 test2
sub1, testA testB
sub1, test1 test2
--- PASS: TestAsyncEventBus_Publish (1.01s)

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